一、Mybatis入门

项目相关包文件的建立：

1.1新建Java项目，导入相关的包

新建一个lib文件，导入基础的包，其中commons-logging-x.x.jar、mybatis-x.x.x.jar、mysql-connector-java-x.x.x-bin.jar是基础包，log4j-x.x.x.jar包和junit-x.x.x.jar包是为了显示日志信息和方便测试使用的包。别忘了Build Path。

1.2建库+表

create database mybatis;
use mybatis;
CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
INSERT INTO users(NAME, age) VALUES('Tom', 12);
INSERT INTO users(NAME, age) VALUES('Jack', 11);

1.3添加Mybatis的配置文件config.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration>
   <environments default="development">
      <environment id="development">
          <transactionManager type="JDBC" />
              <dataSource type="POOLED">
                  <property name="driver" value="com.mysql.jdbc.Driver" />
                  <property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
                  <property name="username" value="root" />
                  <property name="password" value="root" />
           </dataSource>
     </environment>
  </environments>
</configuration>

1.4定义表和表所对应的实体类

这里一定要定义实体类的无参构造方法，否则会报异常。

package com.entity;

public class User {

    private int id;
    private String name;
    private int age;
    public User()
    {
        
    }
    public User(int id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
    
}

1.5定义操作 **user **表的 **sql **映射文件 userMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.config.userMapper">
        <!-- 根据id得到一个user对象 -->
    <!-- 参数类型：parameterType  resultType:结果集类型(全类名)-->
    <select id="getUser" parameterType="int"
        resultType="com.entity.User">
        select * from user where id=#{id}
    </select>
</mapper>

1.6在 **conf.xml **文件中注册 **userMapper.xml **文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
    <!-- 注册映射文件 -->
    <mappers>
       <mapper resource="com/config/userMapper.xml"/>
    </mappers>
</configuration>

1.7编写测试代码：执行定义的 select 语句

package com.test;

import java.io.IOException;
import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.entity.User;



public class Test1 {

    @Test
    public void getUser() throws IOException
    {
        String resource = "config.xml";
        //加载 mybatis 的配置文件（它也加载关联的映射文件）
        Reader reader = Resources.getResourceAsReader(resource);
        //构建 sqlSession 的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
        //创建能执行映射文件中 sql 的 sqlSession
        SqlSession session = sessionFactory.openSession();
        //映射 sql 的标识字符串
        String statement = "com.config.userMapper.getUser";
        //执行查询返回一个唯一 user 对象的 sql
        User user = session.selectOne(statement, 15);
        session.close();
        System.out.println(user);
    }
}